Could Cramping Be Sign Of Pregnancy?

I missed one or two pills duing a week time span but made them both up as soon as I noticed -withing a day of missing each. I was away at the time and when I returned a couple days later, I had sex with my fiance and we did not use the withdrawl method back up as we usually do. From the next morning on I have had unusual cramping, it's been a week now. Could that be a sign of pregnancy? How worried should I be?